Climate Change Triggers Bloodshed

Giving a new definition to "cold war"

THE STUDY“Climate Change and War Frequency in Eastern China Over the Last Millennium,” by David Zhang et al., published in the August 2007 issue of Human Ecology.

THE MOTIVE In a study of more than 900 years of conflict in eastern China, a team of researchers has tested the hypothesis that cold spells fuel the social instability that leads to war.

THE METHODS Earth scientist David Zhang of the University of Hong Kong and his colleagues consulted a multivolume compendium, The Tabulation of Wars in Ancient China, which records wars in China between 800 B.C. and A.D. 1911. They focused on the 899 wars that took place between the years 1000 and 1911 in densely populated eastern China.

The researchers then compared the historical record with climate data for the same period. In the past decade, paleoclimatologists have reconstructed a record of climate change over the last millennium by consulting historical documents and examining indicators of temperature change like tree rings, as well as oxygen isotopes in ice cores and coral skeletons. By combining data from multiple studies, Zhang and his colleagues identified six major cycles of warm and cold phases from 1000 to 1911. The team then tabulated the frequency of wars and grouped them into three classes: very high (more than 30 wars per decade), high (15 to 30 wars per decade), and low (fewer than 15 wars per decade.) All four decades of “very high” warfare, as well as most periods of “high” conflict, coincided with cold phases. The link was most pronounced in the south, perhaps because of its greater population density as well as southern migration due to the cold.

Two especially frigid periods (1448–1487) and (1583–1717) stand out. During the first period, many regions of China suffered huge famines, and authorities of the Ming dynasty quashed rebellions in numerous provinces. At the beginning of the second cold era, heavy rains and severe floods devastated agricultural production, and during the subsequent famine people were forced to eat tree bark and even seeds from the excrement of wild geese. Later, between 1620 and 1640, Earth’s temperature fell to its lowest point since the beginning of the millennium. In China, major floods followed extreme droughts, and frequent famines led to mass starvation and death. In 1644, a peasant rebel leader marched into the capital and captured Beijing. Finally, a Manchu invasion ended the Ming regime.

THE MEANING During warm periods, Zhang explains, populations increased, but the conditions brought on by cold phases—shorter growing seasons, less land available for cultivation, a shortage of forage for domestic animals, and lower agricultural yields—could not sustain them. The shortages fueled peasant unrest, which destabilized regimes. Nearly all China’s dynastic changes took place during the cold spells.

Zhang believes his work has relevance for a warming world. Global temperatures are expected to rise faster and faster in the future, and our expanded population may be unable to adapt to the ecological changes. “Animals can adapt to climate change, mainly by relying on migration, depopulation—which consists of starvation and cannibalism—and dietary change,” he explains. “Human beings have more adaptive choices and social mechanisms, such as birth control, trade, and scientific innovation. Some of these social mechanisms are good for humanity, and some are bad, such as war. The war is just like the cannibalism of animals.”